1. Field of the Invention
The present invention relates to an analytical calculation method of performing analytical calculation using a circuit simulator, and a technique of a circuit simulation model.
2. Description of the Related Art
Clean systems and apparatuses have been developed using a motor as a main power source in order to cope with environmental issues. An inverter is one of converters in a system to be used to drive an alternating-current motor. The inverter is capable of outputting a rectangular wave voltage through a switching operation of a semiconductor element, and simulating a sinusoidal wave having desired frequency and amplitude by superimposing rectangular waves. Accordingly, it is easy to adjust a rotational speed and an output torque of an electric motor, and the efficiency of motor can be significantly improved. Thus, the inverter is a power electronic device which is indispensable to the above-described systems and apparatuses.
A rectangular wave includes a harmonic component, and may be a factor that causes the harmonic component to generate electromagnetic noise. In addition, the rectangular wave is conducted in a circuit of an apparatus as a surge, and influences on voltage endurance properties or insulation properties of components. Meanwhile, an increase in frequency of a switching element has been promoted in order to improve conversion efficiency. Such an increase in frequency leads an increase in generating noise band, which easily influences on other devices. Further, a rising speed of the surge increases, which causes the great influence on the voltage endurance properties or the insulation properties of the components. That is, when the inverter, a cable, and the motor are connected, it is necessary to perform evaluation and design to include the semiconductor element and wiring inductance in the inverter, the cable and the motor such as influence on insulation degradation of the connected motor or radiation noise to be generated from the cable.
Meanwhile, it becomes hard to ignore influence of interaction between a parasitic inductance L of a wiring and a semiconductor element, and accordingly, it becomes hard to suppress an increase in the number of parts and the number of design processes only by relying on experience and know-how as in the related art. Thus, there is an increasing request on a design support through coupled analysis using device simulation and circuit simulation considering the parasite L of the wiring in addition to the device. In addition, there is an increasing request on a model of the device at the time of switching which can be calculated with the coupled analysis using the circuit simulation since the switching of the device becomes sources of generating the noise, the surge and a loss as described above.
A circuit simulator Spice described in “Actual Operation Verification of SPICE Parameter of Power MOSFET”, Shinichi Hashizume, published in Transistor Technology (2000) of the December issue, P275 is generally used in an integrated circuit (IC) and a large-scale integration (LSI) as a simulator to calculate a device and a peripheral circuit. A diode, bipolar transistor, metal-oxide semiconductor field-effect-transistor (MOSEET) used in the IC or the LSI is provided as an equivalent circuit or a model format with standardized behavior. On the contrary, a power device has a larger change with respect to a change in temperature and voltage of an internal state of the semiconductor than that of the device used in the IC or the LSI, and further, the internal state of the semiconductor is nonlinearly changed by receiving influence of an external circuit such as a wiring inductance L, and accordingly, a wave form change thereof is significantly different from an ideal characteristics in a short period of time of the switching. Thus, a standard model for circuit analysis does not exist.
In addition, coupled analysis using device simulation with meshes and circuit simulation is possible in a small circuit, and it is possible to calculate a switching wave form with high accuracy in a device simulator of technology computer-aided design (TCAD) manufactured by Synopsys, Inc. (formerly, ISE Ltd.) described in “Coupled Analysis Simulation. Technique Using Semiconductor Device And Circuit”, Yasushi Abe and Kouji Maruyama, published in Fuji Electric Journal (2003), Vol. 74, No. 4, p 221. However, it takes time for the calculation in the circuit analysis, and thus, an applicable size of the coupled analysis using the circuit simulation is small, and is limited to analysis of the short period of time. Thus, utilization in a circuit of actual electronic machine and equipment including a cable and a motor is difficult. In addition, detailed information including an internal structure of a device is required for the analysis.
In this manner, it is difficult to evaluate influence of the switching wave form of the power device on a product circuit in advance, and thus, the simulation has been used in a review of prototype evaluation.
Meanwhile, there is a technique described in JP-2009-26298-A as a technique of coupled calculation of a wave form of a device at time of switching using circuit simulation. The technique uses either a function formula or broken line approximation, and the function formula is used in the following description. According to the technique, the switching wave form is calculated using the circuit simulation in combination of a function formula of a static characteristic, and a power function formula, a current source function formula, or a non-linear passive element. Although it is difficult to confirm a circuit configuration on a circuit diagram screen like a commercially available circuit simulator as not being a program in circulation, terminals of an inverter arm forms a collector/emitter and a gate terminal. In addition, because this technique is a dedicated program, there is a problem in that it is difficult to utilize a function of a commercially available simulator with high versatility.